This invention relates to setting anchors in masonry or other cementious medium, and more particularly to an anchor that is set in a bore in a cementious member and makes a mechanical connection with the cementious member by cutting into the wall of the bore.
The prior art teaches a number of anchors where the anchor is formed with a stem surrounded by a sleeve, the stem and sleeve being formed so that the stem can be moved in an axial direction with respect to the sleeve, and as the stem slides through the sleeve, ramped surfaces on the stem cause the elongate arms of the sleeve to expand.
If the elongate arms are formed with cutting surfaces that are meant to penetrate into the side wall of the bore as the sleeve expands, then the anchors are said to work by positive engagement rather than by frictional engagement. These anchors, using positive engagement, are believed to secure the anchor in place without causing large radial forces on the sidewall of the bore.
It is believed that friction anchors which do not have cutting edges on the elongate arms and have large surfaces that press against the bore as the sleeve expands subject the sidewall to large radial forces, and thus the material in which the anchor is set must be very strong, such as high strength concrete and strong mineral formations. Further, the bore must be deep enough and the anchor set far enough into the bore that the point where the anchor frictionally engages the sidewall is far removed from the face of the concrete or rock in which the bore is made, to prevent the bursting of the concrete that makes up the sidewall of the bore.
The anchors described above that use positive engagement are more akin to traditional undercut anchors. Traditional undercut anchors are special anchors that are fitted in bores that have special undercuts at their ends, made with a special tool, and the anchor has a flange or shoulder that can be extended to grab the lip of the undercut. In effect, anchors that use positive engagement cut their own lip, on which the cutting edge then hangs, and if only the cutting edge makes contact with the sidewall of the bore, the radial forces on the bore should be localized and limited, because the cutting edge will have cut its way into the sidewall, removing material as it went. Anchors that work by positive engagement with cutting surfaces that are meant to penetrate into the side wall of the bore as the sleeve expands are often called self-undercutting anchors.
The present invention represents an improved positive engagement anchor.